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From: "sjames at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug rtl-optimization/115056] [14/15 regression] Miscompilation
 (also triggering -Wstringop-overflow and -Warray-bounds warning) when -O2 or
 higher
Date: Mon, 13 May 2024 00:57:46 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D115056

--- Comment #7 from Sam James <sjames at gcc dot gnu.org> ---
Isn't there still an uninitialised read?

```
$ valgrind /tmp/foo
[...]
=3D=3D814922=3D=3D
1886221359
1
0
0
0
0
0
=3D=3D814922=3D=3D Use of uninitialised value of size 8
=3D=3D814922=3D=3D    at 0x48F7D3A: _itoa_word (_itoa.c:183)
=3D=3D814922=3D=3D    by 0x49029A6: __printf_buffer (vfprintf-process-arg.c=
:155)
=3D=3D814922=3D=3D    by 0x4904BD0: __vfprintf_internal (vfprintf-internal.=
c:1544)
=3D=3D814922=3D=3D    by 0x49C55AE: __printf_chk (printf_chk.c:33)
=3D=3D814922=3D=3D    by 0x10938D: main (/tmp/foo.c:16)
=3D=3D814922=3D=3D
```

with:
```
#include <string.h>
#include <stdio.h>
typedef union {
        unsigned char as_bytes[64];
        unsigned long long as_chunks[64 / sizeof(unsigned long long)];
} Block;
int main(int argc, char **argv) {
        Block block;
        int i =3D strlen(argv[0]), j =3D 0;
        for (; j < i; j++) block.as_bytes[j] =3D argv[0][j];
        block.as_bytes[j] =3D 0x01; // I removed this line
        while (++j & 7) block.as_bytes[j] =3D 0;
        if (j > 56) while (j < 64) block.as_bytes[j++] =3D 0;
        while (j < 56) block.as_bytes[j++] =3D 0;
        for (j =3D 0; j < 8; j++) printf("%d\n", (int)block.as_chunks[j]);
}
```=